Conceptual help with synching—and ultimately, just how foolproof is it?

***Executive Summary: please give me pointers explaining rabbit holes of synching.*** I have a mental block understanding every little thing about synching, so I can't tell you what it is I'm not yet understanding. *Because I don't understand it fully,* I'm paralyzed from turning it on anywhere, thinking “because I don't fully understand it, if I enable it—NOT knowing its inner workings—I'm going to permanently munge something up royally.” So I'm stuck. I don't want to bog the sub down, so if you have URLs to point to that explain its basics, and then goes into examples of synching between browsers, synching between desktop and laptop, synching between external hard drive and cloud storage, that'd be best. So, please, basically point me to where good learning resources are so I can start clawing my way out of this rabbit hole I'm in. Thanks.